A mobile terminal generally includes antenna switching circuitry for selectively coupling one of a plurality of communication ports to an antenna port in order to transmit or receive a signal. The antenna switching circuitry within a mobile terminal is often prone to receiving electrostatic discharge (ESD). When the received ESD reaches a level high enough to cause damage to the mobile terminal, an ESD event is said to occur. An ESD event may occur due to contact with a user of the mobile terminal, contact with a charged surface, or charge transfer from a nearby electromagnetic field. Because the antenna switching circuitry is coupled to the antenna, the front end receive circuitry, and the front end transmit circuitry within the mobile terminal, an ESD event received at the antenna switching circuitry can cause catastrophic damage to the mobile terminal. Accordingly, ESD protection devices are often included within the antenna switching circuitry to avoid damage to the mobile terminal as a result of an ESD event.
Generally, ESD protection devices are connected to the antenna switching circuitry in a shunt configuration, and are adapted to form a substantially low impedance path to ground during an ESD event in order to safely divert the ESD away from the antenna switching circuitry to ground. FIG. 1 is a schematic representation of antenna switching circuitry 10 including a conventional ESD protection scheme. The antenna switching circuitry 10 includes an antenna port 12, a plurality of communication ports 14, a plurality of switches 16, and a plurality of ESD protection devices 18. For context, an antenna 20 is also shown. The plurality of switches 16 within the antenna switching circuitry 10 are adapted to selectively couple one or more of the communication ports 14 to the antenna port 12 in order to facilitate the transmission and reception of signals.
As shown in FIG. 1, an ESD protection device 18 is coupled to each communication port in the plurality of communication ports 14 in the antenna switching circuitry 10. Accordingly, upon the occurrence of an ESD event on any one of the communication ports 14, the ESD protection device 18 associated with the affected port will safely divert the ESD signal to ground. While effective at protecting a mobile terminal in which the antenna switching circuitry 10 is integrated from damage due to an ESD event, use of the conventional ESD protection scheme may significantly degrade the performance of the antenna switching circuitry 10 and the mobile terminal. Using a separate ESD protection device 18 for each communication port in the plurality of communication ports 14 also consumes a large amount of real estate, thereby increasing the size and cost of the antenna switching circuitry 10. Further, certain communication nodes within the antenna switching circuitry 10 are highly sensitive to distortion, and may be rendered unusable due to the parasitic loading of the connected ESD protection device 18.
Accordingly, ESD protection circuitry is needed that is capable of protecting a mobile terminal from damage due to an ESD event while minimizing the area and parasitic loading introduced by the ESD protection circuitry.